Change from run flats to normal tyres

[Esceptico]

I recently put on new tyres. 17 inch. Existing tyres were run flats but I decided to go with normal tyres (same size) with a can of emergency tyre inflator in the boot (I have breakdown cover too).

Anyway, a day or so after fitting my wife got an error message saying pressure low. I checked and two tyres were a bit low. I pumped them up and reset the warning. Now two weeks later my wife says that the warning is there again and one tyre looks flat (I am going to check when I get home).

I assumed that the alloy wheels I have were not specifically for run flat tyres (I am pretty sure I had a five series in the past and swapped from run flat to normal without any problems). Is there a potential issue in swapping (apart from risk of getting a flat tyre!)?