Not a bug, working as intended, as will become clear below.
Yes you can, matter of fact, you can buy anything as an alpha, whether you can use it or not is probably the more appropriate question.
No there hasn’t and no it doesn’t.
T1 rig BPOs can be bought from the market (as an alpha or not, doesn’t matter).
If you want to build a rig from said BPO you need to look at the manufacturing tab (screen shot from a shield BPO):
As can be seen, industry, + relevant rig skills required (nothing requiring omega).
If you want to improve the material efficiency or time efficiency of the BPO you will need to be Omega, as this requires the metallurgy or research skills, respectively:
This is why the BPO shows up as an “Omega item”, because to do ‘all things’ with the item you do need to have Omega skills.
And finally if you want to copy the BPO so you have BPCs to manufacture from you don’t need any skills!
I hope this puts an end to the confusion.