ARM share price lagging incredibly

ARM were already great value yesterday: around half their NTA based on listed investments and cash. Today they are even better value, by a big margin.
Their biggest investment is PDI in which they hold 572 million shares (source: ARM latest quarterly report). ARM have 116.8million shares in total (source: Iress). Therefore a simple calculation shows that each .1c gain by PDI is worth .49c to each ARM share.
As I write this PDI are up 1.2c today (2.3c). Therefore 1.2 x 4.9 = 5.88 which is the amount that ARM should (theorectically) be up today. However at the current bid price of 8.1c (last sale was at 8c) they are up only 1.1c, less than a fifth of what they should be doing! I know these value situations usually remain at a discount to true worth but this is getting ridiculous. If I ever saw a value proposition (and I have been at this professionally for many decades) this is it.