This is related the driver implementation.
Some chip set organization have implemented a way that 5 Ghz is preferred over 2.4 Ghz.
It's not so it's solely looking at the signal strength, with the cheaper cards it is.
concluding it's very much depending on the implementation of the driver of your Wi-Fi card.
I know with some vendors you can even choose which technology is preferred of the other. (802.11n over 802.11g for example)
What you know see happening in the market is that AP hardware vendors are introducing features like bandsteering.
This means that the AP will wait longer on a client to respond to the sent out management and beacon frames and based on the preference set inside the configuration of the AP steer the client to this standard.
What i mean with this, normally a client will respond to the first available beacon and join, often this means your Wlan card will start the scan at 2.4 Ghz find a network and join this and thus not doing a initial scan at 5 Ghz which is inside the capability of your WLAN card.
With bandsteering (set to 5 Ghz preferred) the AP will wait long on the capabilities of the client and not directly respond the associating request of the client, but also sent out an beacon on the 5 Ghz to see if the client response if it does reconnect at 5 Ghz.
Perhaps HP could implement this band-steering feature soon.
Best regards,
Mike Hydra