Technically it is only legal to enter the Kyrgyz†Republic at a designated entry point. This means that it is no longer possible to trek over the border (for example over Kungei Ala-Too mountains from Almaty in Kazakhstan). More importantly, it is important to receive a stamp in your passport at the border crossing point. This can be important when it comes to registering with OVIR Ц especially if you cross some time after your Kyrgyz visa starts.
If there is no official in passport control or they claim not to have a stamp you can try to make a complaint Ц but you should at least note the date, time and place where you crossed the border. If possible a note of the name and number of any official on duty would also be helpful.
If you have some document Ц such as an airline ticket or a hotel receipt Ц which shows when you were in the other country Ц that might also help Е but the stamp in the passport is the only sure way to avoid potential problems.
Please donТt misunderstand us Е the problem rarely ever arises Ц but it has been known to occur Е and, if possible, you want to avoid it occurring to you.