Stopwatch Bug

Two weeks ago, I noticed something strange. When I use stopwatch, I sell it instantly to buy other items ( I don't have luck to fight AD midlaners, so I don't buy Zhonya's... ). Example: I have 950 gold, I sell it I have 1150 gold. After doing that I clicked on Rabadon's Deathcap and I noticed Needlessly large rod ( or purple rod lol ) was buyable ( idk is that a word lol ). I clicked like idiot for maybe like 15 times, until I noticed I don't have enough gold. So I thought " Hey, let's test this and see am I crazy or not ". I played maybe 20 games ( min pref. ). Same thing. You sell Stopwatch after using it - all items shown are available for buying ( even though you don't have money ). Before asking any questions look at this:

1. I didn't used Rune for debt ( I would not write this article lol );
2. It was not a visual bug ( I tested it, please don't ask how );
3. No I am not Yasuo main nor I will ever be. That's it Riot Games, fix that thing.

'' Boop "