I use a very similar passport case, and like you I keep one or two cards in the back of it - although not money (in my case these cards are only cards that I may need at immigration, such as my US Green Card or my APEC Business Travel Card).

Passport cases, even thin plastic ones, often interfere with the readers that immigration staff use to scan the biographical page on the passport. Many countries I've visited have signage in the immigration area instructing you to remove your passport from its cover before handing it to immigration staff. On more than once occasion when I've failed to do this I've had the officer hand the passport back to me and ask me to remove the case.

Having additional items in the passport cover also leads to the potential that they may be dropped by the agent as they try and remove the passport from the case - in effect your actions are making the officers job more difficult.

Then we come to the money. In general, handing money to an immigration agent is a clear-cut sign that you are attempting to bribe them. This would be the case whether the money was handed to them separately, or within the passport. Having the money "hidden" in the passport doesn't change that fact, it just makes it appear more like you are trying to make the act of bribing the official less obvious.

Once the officer is of the belief that you attempted to bribe them, they will naturally become more suspicious and attempt to determine why you felt the need to bribe them - such as the fact that you may have been using a forged passport.

It doesn't matter whether your intent was to actually bribe the official or not - the fact is that you acted in the exact way that someone that was trying to bribe them would act, so they have to presume that was your intent. I would say that you were very lucky if the only additional action they took was to view your passport with a magnifying glass - it could have ended much worse for you!

I use a very similar passport case, and like you I keep one or two cards in the back of it - although not money (in my case these cards are only cards that I may need at immigration, such as my US Green Card or my APEC Business Travel Card).

Passport cases, even thin plastic ones, often interfere with the readers that immigration staff use to scan the biographical page on the passport. Many countries I've visited have signage in the immigration area instructing you to remove your passport from its cover before handing it to immigration staff. On more than one occasion when I've failed to do this I've had the officer hand the passport back to me and ask me to remove the case.

Having additional items in the passport cover also leads to the potential that they may be dropped by the agent as they try and remove the passport from the case - in effect your actions are making the officers job more difficult.

Then we come to the money. In general, handing money to an immigration agent is a clear-cut sign that you are attempting to bribe them. This would be the case whether the money was handed to them separately, or within the passport. Having the money "hidden" in the passport doesn't change that fact, it just makes it appear more like you are trying to make the act of bribing the official less obvious.

Once the officer is of the belief that you attempted to bribe them, they will naturally become more suspicious and attempt to determine why you felt the need to bribe them - such as the fact that you may have been using a forged passport.

It doesn't matter whether your intent was to actually bribe the official or not - the fact is that you acted in the exact way that someone that was trying to bribe them would act, so they have to presume that was your intent. I would say that you were very lucky if the only additional action they took was to view your passport with a magnifying glass - it could have ended much worse for you!