Rich, that isn't how I understand LTIR to work salary-cap-wise. My understanding is that LTIR provides NO salary cap relief. The salary of the player on LTIR continues to be counted, day by day, toward the salary cap. What DOES happen is that while the player is on LTIR the team gets an exemption to go OVER the salary cap, to bring in a player or players replace him on the roster. The daily exemption is equal to the daily salary of the LTIR player; in Backstrom's case, the daily amount of a $9 million season-long salary. Because Backstrom's salary is so big the team could bring up half a roster of Hershey callus to "replace" him. And that is sort of what they have been doing, with all the guys called up. Then, the day that the LTIR player returns to active status the team loses its exemption and must immediately be in compliance with the Cap, having banked no relief whatsoever from the player's absence. In the Caps' situation, since they started the season tight up against the salary cap with their opening-night roster excluding Backstrom "replacements," they will still be tight up against the cap on the day he returns.
If anyone understands this situation differently than me and has pertinent information about it, please chime in.