Purity - GBL turns into an acid in long-term?

[MrTommyGun]

Hello guys! My uncle used to think he knows everything about GHB, GBL and their chemistry, metabolism whatsoever. However, recently he got really surprised. A few months ago he had come to an idea that the best way of storage and daily usage of GBL is diluting it with water 1:5 and storing it in a glass bottle. He usually measured the required amount of the solution into a cup of juice using a medical dosing cup with 5 ml scaling. Well, everything went smoothly until the point my uncle got out of juice one day and tried to mix his 1:5 GBL solution with a glass of water. It tasted surprisingly acidic. For a purely controlled experiment, he compared this solution with the solution of the same proportion prepared from pure GBL. The tastes were awesomely different. The fresh solution 1:100 had a taste partially astringent with a solid "pepper" flavor. A 1:100 solution prepared by diluting 1:5 solution twentyfold tasted greatly astringent and seriously acidic, but almost completely lacked "pepper". At the same time, the physiological actions were almost the same or barely noticeable.
Ladies and gentlemen, here is the question: what happened to GBL in a 1:5 solution over a span of about one month? Did it convert to GHB-COOH? Or partially to succinic acid? Or semialdehyde? Or?

MrTommyGun added 1389 Minutes and 10 Seconds later...

upd: pH=7